Elena Saiz, C. Cid, A. Guerrero, J. Palacios, Y. Cerrato Space Research Group - Space Weather University of Alcalá (Spain)

 A large depression in the magnetic H-component  It takes place in less than 1 hour  It is a highly local disturbance, showing day (  H 0) asymmetry in longitude  R1 FACs is the current system involved Cid et al. (2015) Abrupt southward turning of IMF Bz (at least 10 nT/min) along with high solar wind pressure ( Saiz et al., to be published soon) a Carrington-like event

 Magnetograms of the H- component at five mid-latitude observatories (  45º MLat) spread in longitude from the INTERMAGNET database  We look for both day/night asymmetry and intensity of the disturbance (  H)  Transients: fast forward shocks with B IMF ratio  4 and/or  V sw  250 km/s as probable sources of H-spike triggers  Database: Heliospheric Shock Database by the University of Helsinki  We look for signatures in a few hours after the shock: ICME sheaths Events 18 October June March April September November July January June September December March 2014

IP GROUND IP GROUND # Events  Bz  10 nT in 1 min? mid-latitude H-spike? 5 out of 12yes 4 out of 12no 3 out of 12yesno YES A couple of examples 24 November 2001 cause - effect 9 out of 12  75% SH: timing shock 21 January 2005

 Hypothesis reinforced with the set of events analysed (75% positive results)  Looking at in longitude, the largest H-spike intensity takes place at the 6-12 MLT sector  Forecasting of these local disturbances becomes a priority Even though interplanetary conditions are met, for developing an H-spike:  is there a minimum time interval  t with negative Bz after a southward Bz turning?  is there a threshold for the negative Bz value?  is there some kind of “coupling” among Bz < 0,  Bz/  t and minimum  t?  or a fluctuating solar wind pressure or a high maintained pressure level? YES NO 31 March 2001 Acknowledgment s. This work has been supported by grants AYA P from the Ministerio de Economía y Competitividad.

# Event  Bz  10 nT in 1 min? (6 h after SH H-spike? 18 October 1995 no 8 June 2000 yesno 31 March 2001 yesno 28 April 2001 yesno 25 September 2001 yes Yes? (MMB (6MLT) pero Pacifico por medio; la  H max = es positiva 24 November 2001 yes Yes.  H max = -260; THY, 9MLT 26 July 2004 yes Yes.  H max = -180; MMB, 9MLT 21 January 2005 yes Yes.  Hmax= -170 and -177; FRN and FRD; 9.5 and 12.5 MLT 12 June 2005 no 12 September 2005 nono (visto en conjunto) 14 December 2006 yes Yes.  H max = -106; FRD, 9.75 MLT 25 March 2014 no